This project involves the application of the SSES methodological approach to the study of basic cognitive and neuropsychological processes and their modulation by the environment. The primary focus of this research is the continuation and expansion of a longstanding collaboration with Dr. Jordan Grafman (Chief Cognitive Neuroscience Section NINDS) centering on the longitudinal Vietnam Head Injury Study (VHIS). Besides this work with Dr. Grafman, we are also completing analyses of data from SSES cognitive psychological experiments carried out before we stopped conducting such research. This year, in our collaboration with Dr. Grafman we used Structural Equation Modeling techniques to categorize the head injured Vietnam veterans into statistically coherent groups in terms of the patterns of their brain injuries. We also collaborated with Dr. Grafman's group in the development of a survey which his group will carry out that will examine the how the interactions between the nature of their head injuries and social structurally determined environmental conditions affect their psychological and psychosocial functioning.